Abstract: A balancing valve has a housing formed with a pair of inlet ports and a pair of coaxial tubes having outer ends seated in the housing at the ports and opposite confronting and axially closed inner ends. The tubes are each formed with a radially throughgoing aperture and a flexible membrane has a center sealingly engaged between and fixed to the inner ends and an outer periphery seated in the housing and defines a respective compartment around each of the tubes. A pair of like sleeves coaxially surrounding the tubes each have an inner end fixed to the membrane offset from the center and from the outer periphery and an outer end. Formations on the outer ends of the sleeves and on the tubes form annular valve openings of flow cross sections dependent on an axial position of the sleeves relative to the tubes.